The invention is the extension of the presently filed patent “A novel via structure for improving signal integrity”, which specifies the method of the improvement of signal integrity in multilayer circuit board. (application Ser. No. 11/651,338). The application of the invention is focused mainly on the combination of multilayer circuit boards by using connectors or any types of interconnection structures.
For the integration of multilayer printed circuit boards (PCB), integrated circuit packages, and integrated circuits on dies, there are many situations in which signals need to switch from circuit board to circuit board. Therefore, a good interconnection structure is needed for the improvement of the signal integrity of the whole system. Typically, a multi-pin connector or IC packaging circuit will be used to connect the signals of two circuit boards. The multi-pin connector connects a PCB to a PCB; the IC packaging circuit connects the die circuit to the PCB.
FIG. 5 to FIG. 20 show four prior situations of interconnection structures. FIG. 5 to FIG. 8 show the first prior interconnection structure. Two signal traces 60, 62 on the top layer of the top PCB 51 switch to the signal traces 61, 63 on the bottom layer of the bottom PCB 52 through the signal vias 70, 71, respectively. The signals propagating along via 70, 71 will pass through the two metal planes 54 and 56 on the top PCB 51, the metal frame 75 of the interconnection structure 53, and the two metal planes 55 and 57 on the bottom PCB 52. The metal planes on both PCBs can be either power planes or ground planes. The metal frame 75 of the interconnection structure 53 will connect electrically to the metal planes on both PCBs 51, 52 through the ground via (or power via) 69. When the signals propagate through via 70, 71, they will generate electromagnetic (EM) waves. The EM waves will not penetrate through the two ground vias (or power vias) 64 and 66 on the top PCB 51, the two ground vias (or power vias) 65 and 67 on the bottom PCB 52 and the metal frame 75 of the interconnection structure 53. However, the EM waves will leak from the junctions of the two PCBs 51, 52 and of the interconnection structure 53 due to the discontinuity between the two ground vias (or power vias) 64 and 66 on the PCBs 51, 52 and the metal frame 75 of the interconnection structure 53. The leakage of the EM waves will degrade the signal integrity. Also, the impedances of the signals propagating in the vias on the PCBs will be different from that of the signals propagating in the vias of the interconnection structure. This is the so-called impedance discontinuity. This impedance discontinuity will affect the signal quality as well. The ground via (or power via) 69 connects electrically to the ground planes (or power planes) on both PCBs and the metal frame 75 of the interconnection structure 53. It provides a current return path for the signals. However, the current return path is not the shortest current return path for the signals. Therefore, it will improve the signal integrity only a little.
FIG. 9 to FIG. 12 show the second prior interconnection structure. Two signal traces 119, 122 on the top layer of the top PCB 110 switch to the signal traces 121, 124 on the bottom layer of the bottom PCB 111 through the signal vias 120, 123, respectively. The signals propagating along vias 120, 123 will pass through the two metal planes 113 and 115 on the top PCB 110, the metal frame 130 of the interconnection structure 112, and the two metal planes 114 and 116 on the bottom PCB 111. The metal planes on both PCBs can be either a power plane or ground plane. The metal frame of the interconnection structure connects electrically to the metal planes on both PCBs through the ground via (or power via) 126. When the signals propagate through the signal vias 120, 123, they will generate electromagnetic (EM) waves. Due to the lack of ground vias or power vias surrounding the signal vias on the PCBs, the EM waves will propagate between the two metal planes 113 and 115 on the top PCB 110 and the two metal planes 114 and 116 on the bottom PCB 111. The EM waves propagating between metal planes will cause voltage fluctuations that will degrade the signal integrity. Also, the EM waves will leak from the junctions of the two PCBs 110, 111 and the interconnection structure 112. The leakage of the EM waves will degrade the signal integrity. Again, the impedance of the signals propagating in the vias on the PCBs will be different from that of the signal propagating in the vias of the interconnection structure. This is the so-called impedance discontinuity. This impedance discontinuity will affect the signal quality as well. The ground via (or power via) 126 connects electrically to the ground planes (or power planes) on both PCBs 110, 111 and the metal frame 130 of the interconnection structure 112. It provides a current return path for the signals. Again, it will improve the signal integrity only a little because the current return path is not the shortest current return path for the signals.
FIG. 13 to FIG. 16 show the third prior interconnection structure. Two signal traces 160, 163 on the top layer of the top PCB 151 switch to the signal traces 162, 165 on the bottom layer of the bottom PCB 152 through the signal vias 161, 164, respectively. The signals propagating along vias 161, 164 will pass through the two metal planes 154 and 156 on the top PCB 151, the metal frame 172 of the interconnection structure 153, and the two metal planes 155 and 157 on the bottom PCB 152. The metal planes on both PCBs can be either power planes or ground planes. The metal frame 172 of the interconnection structure 153 does not connect electrically to the metal planes on both PCBs. When the signals propagate through vias 161, 164, they will generate electromagnetic (EM) waves. Due to the lack of ground vias (or power vias) surrounding the signal vias on the PCBs, the EM waves will propagate between the two metal planes 154 and 156 on the top PCB 151 and the two metal planes 155 and 157 on the bottom PCB 152. The EM waves propagating between metal planes will cause voltage fluctuations that will degrade the signal integrity. Also, the EM waves will leak from the junctions of the two PCBs 151, 152 and of the interconnection structure 153. The leakage of the EM waves will degrade the signal integrity. Also, the impedance of the signals propagating in the vias on the PCBs will be different from that of the signals propagating in the vias of the interconnection structure 153. This is the so-called impedance discontinuity. This impedance discontinuity will affect the signal quality as well. The ground via (or power via) 167 connects electrically to the ground planes (or power planes) on both PCBs but does not connect electrically to the metal frame 172 of the interconnection structure 153. Therefore, the ground via (or power via) 167 will only provide a long current return path for the signals. It will benefit the signal integrity very little.
FIG. 17 to FIG. 20 show the fourth prior interconnection structure. Two signal traces 210, 213 on the top layer of the top PCB 201 switch to the signal traces 212, 215 on the bottom layer of the bottom PCB 202 through the signal vias 211, 214, respectively. The signals propagating along vias 211, 214 will pass through the two metal planes 204 and 206 on the top PCB 201, the interconnection structure 203, and the two metal planes 205 and 207 on the bottom PCB 202. The metal planes on both PCBs can be either power planes or ground planes. There is no metal frame for the interconnection structure. When the signals propagate through via 211, 214, they will generate electromagnetic (EM) waves. Due to the lack of ground vias or power vias surrounding the signal vias on the PCBs, the EM waves will propagate between the two metal planes 204 and 206 on the top PCB 201 and the two metal planes 205 and 207 on the bottom PCB 202. The EM waves propagating between metal planes will cause voltage fluctuations that will degrade the signal integrity. Also, because there is no metal frame in the interconnection structure 203, the EM waves will propagate outward along the interconnection structure 203 and the EM waves will couple each other between signal vias easily. This coupling will increase the insertion losses of the signals. Also, the impedance of the signals propagating in the signal vias 211, 214 on the PCBs will be different from that of the signal propagating in the signal vias 211, 214 of the interconnection structure 203 due to the material difference between the PCB 201, 202 and the interconnection structure 203. This is the so-called impedance discontinuity. This impedance discontinuity will affect the signal quality as well. The ground via (or power via) 217 only connects electrically to the ground planes (or power planes) on both PCBs. It will provide a long current return path for the signals. It will benefit the signal integrity very little.
The coarse solid lines A1, A2 of FIGS. 21 and FIG. 22 show the simulated insertion losses (S21 and S43) of the signal paths indicated from FIG. 1 to FIG. 4 for the novel interconnection structure. The other dashed lines and thin solid lines of FIG. 21 and FIG. 22 show the simulated insertion losses (S21 and S43) of the signal paths indicated from FIG. 5 to FIG. 20 for the four prior interconnection structures. The insertion losses (S21 and S43) of the coarse solid lines A1, A2 are larger than those of the other dashed lines and thin solid lines. The smaller insertion loss values for the four prior interconnection structures indicate that there is more energy dissipated along the signal paths. These energy losses could be due to EM radiation, impedance discontinuity, dielectric loss, and so on.
The coarse solid lines A3, A4 of FIGS. 23 and FIG. 24 show the simulated insertion losses (S31 and S42) of the signal paths indicated from FIG. 1 to FIG. 4 for the novel interconnection structure. The other dashed lines and thin solid lines of FIG. 23 and FIG. 24 show the simulated insertion losses (S31 and S42) of the signal paths indicated from FIG. 5 to FIG. 20 for the four prior interconnection structures. The insertion losses (S31 and S42) of the coarse solid lines A3, A4 are smaller than those of the other dashed lines and thin solid lines. The smaller insertion loss values for the novel connectors indicate that there is less energy coupled between the signal paths.